1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a light emitting apparatus for use in the image forming apparatus, and more particularly to an image forming apparatus in which a plurality of photosensitive members are arranged linearly and are used independently of one another to form cyan, magenta, yellow and black images on respective photosensitive members, these images being combined to form a color image.
2. Description of the Related Art
There is known a laser-source image forming apparatus constructed as follows. Four laser-beam light sources are provided as image exposure means respectively for four electrophotographic photosensitive members arranged linearly, and oscillation of the light sources is controlled in accordance with respective image information for cyan, magenta, yellow and black colors to form cyan, magenta, yellow and black electrostatic latent images on the four electrophotographic photosensitive members in a one-to-one relation. These latent images are developed and the resulting developed images are combined to form a color image.
An LED-source image forming apparatus is also known which employs, as light sources for forming cyan, magenta, yellow and black electrostatic latent images, four LED light sources disposed for illuminating respective photosensitive members, instead of the above-described laser-beam light.
At the present state of art, however, the laser-source image forming apparatus has difficulty in controlling the four laser-beam light sources disposed respectively for the four photosensitive members to emit laser beams in an exactly aligned relation with each other in both the direction of main scan and the direction of sub-scan so that cyan, magenta, yellow and black images are combined in alignment with each other to create a desired color image.
On the other hand, the LED-source image forming apparatus can relatively easily meet the requirement of emitting rays of light in an exactly aligned relation with one another in both the direction of main scan and the direction of sub-scan, but experiences other problems. Particularly, the apparatus is expensive because LEDs are themselves relatively expensive and, in addition, an LED light source requires a linked LED device comprising a plurality of LED chips linked to each other linearly. These LED chips differ in luminescent characteristics from one chip to another, and such a linked LED device is used to expose an image forming area in the direction of main scan across movement of the photosensitive member. This causes exposure conditions to differ depending on the luminescent characteristics of individual chips, resulting in poor image reproducibility in the direction of main scan.
In an electrophotographic copying machine adapted for forming a color image, it is required to arrange the linked LED device for each of a plurality of photosensitive members. In such a color copying machine, the plurality of linked LED devices disposed for respective photosensitive members also differ in their luminescent characteristics. This situation results in a severe demand for proper adjustment of luminescent characteristics between linked LED devices disposed to illuminate respective photosensitive members in a one-to-one relation.